Reducing the gel effect in free radical polymerization

The gel effect is a phenomenon that often takes place during a free radical polymerization at intermediate or high degrees of conversion. It consists of the autoacceleration of the rate of the polymerization and it is due to diffusion limitations that slow down the termination reaction leaving the propagation and the initiation reactions unaffected. This phenomenon is highly undesired in industrial application because it causes a fast and dramatic increase of the temperature of the reacting medium, often leading to scale-up problems, instabilities, hot spots, and erratic behavior. In this paper, we present the results of kinetic experiments performed in a cone and plate rheometer with two common monomers: styrene and n-butylmethacrylate. We show that the gel effect can be significantly reduced, if not eliminated,performing the polymerization at high shear rate. A new experimental device, the helical barrel rheometer, has been used and some preliminary results are presented. (C) 2001 Elsevier Science Ltd. All rights reserved.